This specification relates to data processing and content distribution.
The Internet provides access to a wide variety of resources. For example, video and/or audio files, as well as web pages for particular subjects or particular news articles are accessible over the Internet. Access to these resources presents opportunities for content items to be provided with the resources and presented in content item slots. For example, a web page can include advertisement slots in which advertisements can be presented. These advertisements slots can be defined in the web page or defined for presentation with a web page.